Aquatic Microbiology

Aquatic Habitats & Microbes - Diverse Water Worlds

• Freshwater Systems:
  • Lakes (lentic): Exhibit thermal stratification.
    • Epilimnion (surface): Aerobic; cyanobacteria, algae, heterotrophic bacteria.
    • Hypolimnion (bottom): Anaerobic; methanogens, sulfate-reducers.
  • Rivers (lotic): Dynamic; biofilms on surfaces, influenced by terrestrial input.
• Marine Systems:
  • Oceans: Vast, diverse zones.
    • Photic zone: Dominated by phytoplankton (e.g., Prochlorococcus, diatoms), viral lysis common.
    • Aphotic/Deep sea: High pressure (piezophiles), low temperature (psychrophiles); chemolithoautotrophy at hydrothermal vents.
  • Estuaries: Brackish, fluctuating salinity; high microbial activity.
• Groundwater: Often oligotrophic; unique chemolithoautotrophs.

⭐ Prochlorococcus, a picocyanobacterium, is the smallest and most abundant photosynthetic organism on Earth, responsible for a large fraction of marine primary production.

Water Quality & Indicators - Tiny Health Monitors

• Indicator Organisms: Microbes whose presence signals potential faecal contamination & associated pathogens.
  • Ideal: Easy to detect, non-pathogenic, survives like pathogens, faecal-specific.
• Key Indicators:
  • Total Coliforms: General hygiene indicator.
  • Faecal Coliforms: Thermotolerant (grow at 44.5°C), indicate faecal origin.
  • Escherichia coli: Specific to faecal contamination; most reliable.
  • Faecal Streptococci (Enterococci): Indicate faecal pollution, more resistant.
  • Clostridium perfringens: Spores indicate past/intermittent pollution.
• Testing Methods:
  • MPN (Most Probable Number): Estimates density.
  • Membrane Filtration: Direct viable count.
  • Presence-Absence Test.
  • IMViC: Differentiates E. coli.

⭐ Escherichia coli is the most reliable indicator of recent faecal pollution in drinking water due to its exclusive faecal origin and shorter survival time outside the host.

Waterborne Pathogens - Invisible Threats Lurking

Contaminated water harbors diverse pathogens. 📌 Key Types: Bacteria, Viruses, Protozoa.

• Bacteria:
  • Vibrio cholerae: Cholera ("rice-water stools", severe dehydration)
  • Salmonella typhi: Typhoid fever (step-ladder pyrexia, rose spots)
  • Shigella spp.: Shigellosis (bacillary dysentery, tenesmus)
  • E. coli (ETEC, EHEC): Diarrhea (traveler's, HUS from O157:H7)
  • Campylobacter jejuni: Gastroenteritis (common, Guillain-Barré link)
  • Leptospira interrogans: Leptospirosis (Weil's disease: jaundice, renal failure)
• Viruses:
  • Hepatitis A & E: Acute viral hepatitis (fecal-oral)
  • Rotavirus: Severe infantile diarrhea (vaccine-preventable)
  • Norovirus: Epidemic gastroenteritis ("winter vomiting bug")
• Protozoa:
  • Giardia lamblia: Giardiasis (foul-smelling steatorrhea, "beaver fever")
  • Entamoeba histolytica: Amoebiasis (dysentery, liver abscess)
  • Cryptosporidium parvum: Cryptosporidiosis (watery diarrhea, severe in AIDS CD4 < 100)

⭐ Hepatitis E virus (HEV) infection in pregnant women (3rd trimester) carries high mortality (up to 20-30%).

Biofilms & Water Treatment - Slime & Shine

• Biofilms: Structured microbial communities encased in self-produced Extracellular Polymeric Substance (EPS), offering protection.
  • Formation Stages: Attachment → Colonization (Quorum Sensing vital) → Maturation (complex 3D architecture) → Dispersal.
  • Significance: ↑ Antimicrobial resistance (e.g., Pseudomonas), persistent infections, medical device/pipe biofouling.
• Water Treatment Process: Essential multi-barrier approach for safe drinking water.

-   Key Disinfection Methods:
    -   Chlorination: Must achieve breakpoint for adequate free residual chlorine.
    -   UV Radiation: Damages microbial DNA, preventing replication.
    -   Ozone ($O_3$): Powerful, broad-spectrum oxidizing agent.

⭐ Breakpoint chlorination is critical: chlorine demand satisfied, further addition gives proportional free residual chlorine (target 0.2-0.5 mg/L) for sustained disinfection. 📌 Smart Chemists Study Fluids Diligently (Screening, Coagulation, Sedimentation, Filtration, Disinfection)

High‑Yield Points - ⚡ Biggest Takeaways

• Indicator organisms (e.g., E. coli) signal fecal contamination and assess water quality.
• Key waterborne diseases: cholera, typhoid, hepatitis A/E, shigellosis.
• Biofilms in water systems harbor pathogens, aiding antimicrobial resistance.
• Eutrophication causes algal blooms; some produce cyanotoxins.
• Legionella pneumophila in water systems causes Legionnaires' disease.
• Leptospirosis is transmitted via water contaminated with infected animal urine.
• Water purification (chlorination, filtration) is vital for disease prevention.